Technical Abstract:
Management of prickly pear on rangelands has lead to numerous studies aimed at understanding prickly pear response to various natural and human induced treatments. Information is lacking on Plains prickly pear response to varied fuel loads. Pads of clones from three soil types (claypan, gravel, silt) were subjected to fire with two weather conditions (22oC and 37% RH; 36oC and 27% RH) at four fuel loads (1500 – 6000 kg ha*-1) and a non-burned control. Fires were conducted using field-collected grass in a burn cage and time-temperature curves were developed from thermocouples at the soil surface and 8 cm above the surface. Burned pads were returned to the greenhouse and watered weekly and monitored for pad mortality and resprouting. Fuel load explained 55% of variation in heat dosage. Maximum temperature, duration, and degree-seconds all increased as fuel loads increased. Mortality of initial pads was about 13% for non-burned plants, 54% with 1500 kg ha*-1, and 96% with 3000 kg ha*-1 or more fuel. Total plant mortality was less because of new pads sprouting, but increased 9% for each additional 1000 kg ha*-1 of fuel, with a maximum mean plant mortality of 63%. Fuel load and fire duration are important predictive variables in determining prickly pear mortality. Although mortality can be achieved with moderate fuel loads, potential for resprouting under greenhouse conditions occurred across all fuel treatments.